In some applications it is desirable or even necessary to be aware of an interruption of electrical power to a particular electronic device. For example, semiconductor memory devices are power sensitive in that, if supply voltage is reduced below some threshold value, or is completely removed, the data stored within the memory is destroyed. Similarly, a computer or microprocessor stores data temporarily in its register structure which, in the event of a power fluctuation or removal may be destroyed.
In certain applications, particularly those wherein the operation of a device of concern is not continually monitored, a temporary reduction or loss of power may not be noticed by the operator. A subsequent attempt to utilize the device may result in manipulation of incorrect data. For example, a semiconductor memory module or processor which is maintained for long periods of time without actual use, and which may be operated during this period by a battery source of supply (an automobile engine control device, for example) may, when it is put back into use, contain or operate upon incorrect data. It is desirable that a user or operator of such a device be able to determine whether any fluctuation or interruption has occurred to the source of power. The operator can then take appropriate action such as reloading the data into a memory or resetting the microprocessor internal registers.